1. Field of the Invention
This invention relates to a drilling device for boring holes in a rigid material of a stone, concrete or the like while applying atomized water to the cutting bit of a drill, and more particularly to a mist-spouting type drilling device capable of cooling the cutting bit by spouting atomized water through a mist passage in the drill shank so as to efficiently bore a hole in the rigid material.
2. Description of the Prior Art
When boring a hole in a rigid material such as a stone and concrete by use of a drill with a cutting bit made from ultra-hard abrasive grains including diamond grains or the like, the cutting bit is heated and reaches as high as about 300.degree. C. to 600.degree. C. due to the heat of rolling friction caused between itself and the rigid material. The frictional heat generated in drilling increases remarkably the wear rate of the cutting bit thereby to shorten the life of the drill.
In order to prevent the cutting bit of the drill from reaching a high temperature in drilling, there have conventionally been employed various methods for cooling the cutting bit by use of a spout of water or air. In these methods, a hollow drill having an axial fluid passage is used and a cooling fluid such as water and air is spouted from the leading end of the drill through the axial fluid passage, thereby cooling effectively the cutting bit of the drill.
In the conventional drilling devices, a water-cooling method using water as coolant has an effect of sufficiently cooling the cutting drill. However, it entails a disadvantage in that the material to be bored and the circumferences thereof are considerably stained with the water spouted from the drill. If a hood cover encircling the drill is used for recovering the water spouted from the leading end of the drill, it adds to the size and complexity of the drilling device and renders the handling of the device difficult.
An air-cooling method of the drilling device, in which air is spouted from the leading end of the drill, cannot be expected to sufficiently cool the cutting bit. Furthermore, according to this method cutting chips produced in drilling are carried about in the air. Thus, an attempt has been made to prevent the cutting chips from being scattered in the air by use of an encircling cover for collecting cutting chips. It nevertheless suffers from operational inefficiency.
There has been a need for a drilling device having the distinctive features of the conventional drilling devices of the water-cooling type and air-cooling type which have opposite effects to other--namely, a drilling device having an effect of efficiently cooling the cutting bit and being easy to handle.